Coherent suppression of picosecond magnetization precession in the presence of spin waves in a Ni₈₁ Fe₁₉ microstripe

We present the experimental and micromagnetic simulation studies of coherent suppression of picosecond magnetization precession in Ni₈₁ Fe₁₉ (Permalloy) microstripes with widths of 5, 10, and 12 μm and length of 100 μm in the presence of multiple spin wave modes. The lateral confinement of the microstripes causes spin wave modes of frequencies adjacent to each other, and the local suppression of the modes was experimentally achieved with field pulses of slightly different durations but with same rise time and fall time. Micromagnetic simulations show that application of the pulse field causes a large angle (∼135°) reorientation of the magnetization, followed by a precession. At a particular value of pulse duration (suppression time), the magnetization returns back to the equilibrium position and suddenly becomes parallel to the effective field so that the torque on the magnetization vanishes. However, this applies to localized regions due to the presence of spin wave modes of slightly different frequencies along the short axis of the microstripe. Pulses of little under- or overwidth cause the precession to continue at a slightly different frequency, suggesting that the spin wave modes are not truly localized but there are overlapping regions where one mode dominates but the other modes appear more prominently when the dominating mode is suppressed. For stripes of different widths, similar spatial dependence of suppression time was observed. However, the average value of the suppression time decreases with reduced width of the stripe as a result of the increase in precession frequency.